Acoustic driven toughened foam glass abrasive devices and a method for producing the same

ABSTRACT

An abrasive tool having an elongated handle member, an ultrasonic vibration source operationally connected to the elongated handle member, and a toughened foamed glass ceramic portion operationally connected to the vibration source. The toughened foamed glass ceramic portion includes a first glassy phase and a second glassy phase, wherein the second glassy phase puts the first glassy phase into compression.

TECHNICAL FIELD OF THE INVENTION

The invention relates generally to the field of ceramic abrasives and, specifically, to a method and apparatus for using toughened foamed glass ceramic materials in abrasive tool surface applications.

BACKGROUND OF THE INVENTION

Foamed glass is an established lightweight ceramic material. Typically, foamed glass is made in one of two ways. The first way involves preparing a stable foam from water and foaming agent, preparing a wet mixture or slurry of solid components (where cement is the main substance), quick mixing the foam and the slurry, filling molds with prepared the mixted foam/slurry, and firing the same. The second way to make foamed glass involves making use of the property of some materials to evolve a gas when heated. A foamed glass material may be prepared by mixing crushed glass particles and a foaming agent (such as CaCO₃ or CaSO₄), placing the mixture in a mold, heating the mold (such as by passing the mold through a furnace) to a foaming temperature, and cooling the mold to produce foamed glass bodies.

While useful as insulation and abrasive materials, foamed glass bodies are still relatively fragile. This is especially true when the foamed glass materials are used as abrasive materials. Foamed glass abrasives offer the advantage of being easily ablative and thus relatively mild abrasives. However, there is a gap between the easily ablated foamed glass materials and traditional hard and tough ceramic abrasives. Thus, there remains a need for a tougher foamed glass material. The present invention addresses this need.

SUMMARY OF THE INVENTION

The present invention relates to a process for the manufacturing toughened foamed glass materials, and vibratory abrasive tools made from the same. One object of the present invention is to provide an improved foamed glass material. Related objects and advantages of the present invention will be apparent from the following description.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of a block of foamed glass.

FIG. 2 is a schematic view of a method for producing toughened foamed glass according to the present invention.

FIG. 3A is a perspective view of a first embodiment acoustic abrasive device according to the present invention.

FIG. 3B is a perspective view of a second embodiment acoustic abrasive device according to the present invention.

FIG. 3C is a perspective view of a third embodiment acoustic abrasive device according to the present invention.

FIG. 3D is a perspective view of a fourth embodiment acoustic abrasive device according to the present invention.

FIG. 3E is a perspective view of a fifth embodiment acoustic abrasive device according to the present invention.

FIG. 3F is a perspective view of a sixth embodiment acoustic abrasive device according to the present invention.

FIG. 3G is a perspective view of a seventh embodiment acoustic abrasive device according to the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

For the purposes of promoting an understanding of the principles of the invention and presenting its currently understood best mode of operation, reference will now be made to the embodiments illustrated in the drawings and specific language will be used to describe the same. It will nevertheless be understood that no limitation of the scope of the invention is thereby intended, with such alterations and further modifications in the illustrated device and such further applications of the principles of the invention as illustrated therein being contemplated as would normally occur to one skilled in the art to which the invention relates.

White foamed glass (see FIG. 1), in its most simple form, is manufactured by heating a mixture of clear glass powder and a foaming agent (such as limestone) to a temperature sufficient to release the loosely bound gas from the foaming agent (such as the conversion of limestone to lime and carbon dioxide). The foam is produced as the gas is released from the foaming agent and diffuses through the viscous (γ≅10⁴⁻⁵ Pa*s) melting glass particles/molten mass to form individual cells and/or pores. The resultant glass foam body 10 is then cooled and shaped into as desired. Drywall is an example of a product made thusly from foamed glass. Sometimes, additional chemicals are added to the glass and foaming agent batch to enhance particularly desirable physical properties (such as abrasiveness, resistance to wear, density, color, etc.).

As illustrated in FIG. 2, a foamed glass or cellular ceramic material may be toughened or made more wear-resistant by developing compressive stresses in the foamed glass during fabrication. These stresses are induced by the addition of a predetermined smaller concentration of a second glass frit material 22 to the first or base glass frit material 20 in the batching stage 15, whereupon the batch is intimately mixed 25. The first or base glass frit material 20 is typically a soda-lime silica (Na₂O—CaO—SiO₂) glass. Typically, the first glass frit material 20 is composed of a powdered glass cullet, more typically of powdered window, plate and/or bottle glass, although other glass cullet sources may be used. The second or toughening glass frit material 22 typically has a lower coefficient of thermal expansion (CTE) than the base material, and typically substantially retains its chemical identity during the foaming process.

The average particle size (diameter) of the frits 20, 22 is typically between about 8-10 microns, although frits of other particle sizes may also be used. In some applications, the PSD (particle size distribution) of the frits 20, 22 may be bimodal, with peaks at about 8 and at about 10 microns; in other applications, the PSD may be trimodal with peaks at about 8, about 10, and about 100 microns. By controlling the PSD, the cell size distribution and/or porosity of the resultant foamed glass may be better controlled.

The foaming agent 26 is typically limestone or calcium carbonate (CaCO₃), magnesite (MgCO₃) and/or carbonic acid (SrCO₃). The choice of foaming agent 26 may also influence the foaming, porosity and/or cell structure of the resulting foamed glass body 20. The different foaming agents 26 release their carbon dioxide at different temperatures and may thus be used to foam glass compositions with different softening points of used in combination to vary the rate at which carbon dioxide gas is evolved. For example, the substitution of calcium carbonate with magnesite results in foamed glass bodies 10 having relatively large pores and/or increased foam height.

Predetermined amounts of the first and second frits 20, 22 are mixed to form a batch 32. A predetermined amount of foaming agent 26 is also mixed into the batch 32. After mixing, the batch 32 is portioned 33 into one or more molds 34, and then fired 38 to a temperature sufficient to soften or melt the frits 20, 22 and release the bound gas from the foaming agent 26. The firing temperature and/or the rate at which the batch portion 33 is fired 38 may be varied to control the foaming of the glass (i.e., by varying the temperature and firing profile), the viscosity of the glass and the rate at which gas evolves from the foaming agent 26 may be controlled, thus controlling the foaming of the glass; by ramping faster to higher temperatures, the viscosity of the glass may be decreased while the foaming agent rapidly evolves gas, thus resulting in more vigorous foaming. Conversely, by heating more slowly or to a lower temperature, foaming may be kept more subdued and thus minimized.)

The resultant glass foam 40 may then be cooled, whereupon the dispersed lower CTE phase contracts less than the higher CTE base phase matrix, putting the base phase matrix in compression and thus rendering the base phase more wear resistant. The toughened foamed glass body 10 may be molded to shape, or pieces 42 may be cut to shape from a block 10 of foamed glass material. The wear resistant glass foam pieces 42 may be incorporated into an abrasive device 50, such as by connecting the toughened foamed glass abrasive material 42 to an acoustic or vibratory source 52 (see FIGS. 3A-3G).

While the invention has been illustrated and described in detail in the drawings and foregoing description, the same is to be considered as illustrative and not restrictive in character. It is understood that the embodiments have been shown and described in the foregoing specification in satisfaction of the best mode and enablement requirements. It is understood that one of ordinary skill in the art could readily make a nigh-infinite number of insubstantial changes and modifications to the above-described embodiments and that it would be impractical to attempt to describe all such embodiment variations in the present specification. Accordingly, it is understood that all changes and modifications that come within the spirit of the invention are desired to be protected. 

1. A method of fabricating an abrasive tool with a toughened foamed glass ceramic abrasive surface, comprising the steps of: a) combining a first predetermined amount of a first frit and a second predetermined amount of a second frit to produce a batch; b) adding a third predetermined amount of foaming agent to the batch; c) mixing the batch; d) placing a fourth predetermined amount of the batch into a mold; e) heating the mold to a predetermined temperature; f) cooling the mold; g) removing a foamed glass abrasive body from the mold; and h) operationally connecting the foamed glass abrasive body to a handle; wherein the first frit is characterized by a first coefficient of thermal expansion; wherein the second frit is characterized by a second coefficient of thermal expansion; and wherein the first coefficient of thermal expansion is higher than the second coefficient of thermal expansion.
 2. The method of claim 1 wherein the first and second frits substantially maintain their respective chemical identities when the mold is heated.
 3. The method of claim 1 wherein the first frit is powdered window glass.
 4. The method of claim 1 wherein the foaming agent is limestone.
 5. The method of claim 1 wherein the foaming agent is a mixture of limestone and magnesite.
 6. The method of claim 1 wherein the handle is connected to a vibratory source.
 7. The method of claim 1 wherein the handle further comprises an ultrasonic acoustic source.
 8. A method of producing a toughened foamed glass body, comprising: a) combining a first predetermined amount of powdered window glass cullet with a second predetermined amount of powdered toughening glass cullet to define a batch; b) adding a third predetermined amount of foaming agent to the batch; c) mixing the batch; d) apportioning the batch; e) softening the glass; f) releasing gas from the foaming agent to foam the softened glass; g) cooling the foamed glass body; wherein the window glass cullet is characterized by a higher coefficient of thermal expansion than the toughening glass cullet.
 9. The method of claim 8 wherein the glass is softened and gas is released from the foaming agent as a result of firing the batch.
 10. The method of claim 8 wherein the window glass and the toughening glass do not substantially chemically interact.
 11. The method of claim 9 wherein the foaming agent is selected from the following compositions: CaCO₃, MgCO₃ and SrCO₃.
 12. The method of claim 8 wherein batch is apportioned by at least partially filing a refractory vessel and wherein the glass is softened and gas is released from the foaming agent as a result of firing the refractory vessel.
 13. An abrasive tool, comprising in combination: an elongated handle member; an ultrasonic vibration source operationally connected to the elongated handle member; and a toughened foamed glass ceramic portion operationally connected to the vibration source; wherein the toughened foamed glass ceramic portion includes a first glassy phase and a second glassy phase; and wherein the second glassy phase puts the first glassy phase into compression.
 14. The system of claim 13 wherein the first glassy phase is substantially soda-lime-silica glass characterized by a first coefficient of thermal expansion and wherein the second glassy phase is characterized by a second coefficient of thermal expansion that is substantially smaller than the first coefficient of thermal expansion. 